/Engine/Source/Runtime/GeometryCore/Public/VectorUtil.h
Tan(theta/2) = +/- sqrt( (1-cos(theta)) / (1+cos(theta)) )
positive value of tan(theta/2) where theta is angle between normalized vectors A and B
namespace UE { namespace Geometry { namespace VectorUtil { template<typename RealType> RealType UE::Geometry::VectorUtil::VectorTanHalfAngle ( const [TVector](API\Runtime\Core\Math\TVector)< RealType > & A, const [TVector](API\Runtime\Core\Math\TVector)< RealType > & B ) } } }